1. Field of the Invention
The present invention relates to a scroll-type fluid machine suitable for a compressor for fluid such as air, a vacuum pump, an expansion device, and the like.
2. Description of the Related Art
In general, a scroll-type fluid machine can be categorized into a compressor compressing fluid such as air or refrigerant, a vacuum pump depressurizing an interior of a container, an expansion device expanding fluid, and the like. This type of the scroll-type fluid machine generally comprises: a casing; a fixed scroll fixed to the casing wherein a spiroid lap portion is standing on a surface of an end plate; an orbiting scroll provided with a spiroid lap portion standing on a surface of an end plate, the orbiting scroll forming a plurality of fluid chambers so as to compress or expand fluid between the fixed scroll and the orbiting scroll through orbiting motion; a driving shaft rotatably provided within the casing so as to allow the orbiting scroll to move in an orbital manner; and an auxiliary crank device provided between the casing and the orbiting scroll so as to prevent the orbiting scroll from being rotated. See, for example, Japanese Patent Application Laid-Open No. H11-82328 (hereinafter referred to as the patent document 1).
In conventional scroll-type fluid machines, spiral lap portions are each provided on surfaces of end plates composed of a fixed scroll and an orbiting scroll, whereby a plurality of fluid chambers are formed by superimposing each of the lap portions one another. Further, in the scroll-type fluid machines, the orbiting scroll is moved in an orbital manner through a driving shaft by means of a driving source such as a motor. Accordingly, fluid such as air or refrigerant can be sequentially compressed within each of the fluid chambers.
Furthermore, an auxiliary crank device comprises: a fixed-side bearing portion provided with a casing; an orbiting-side bearing portion provided with the orbiting scroll; and an auxiliary crank shaft, one side of which is rotatably supported with the fixed-side bearing portion while the other side of which is rotatably supported with the orbiting-side bearing portion. Here, eccentric measurements of the one side and the other side of the auxiliary crank shaft are set identical with an orbiting radius where the orbiting scroll moves in an orbital manner. Accordingly, the auxiliary crank device can prevent the orbiting scroll from being rotated when the orbiting scroll moves in an orbital manner.
Considering the conventional scroll-type fluid machines, centrifugal force will be generated along with orbiting motion of the orbiting scroll. This centrifugal force of the orbiting scroll is separately supported by bearings of the driving shaft and the auxiliary crank device. Accordingly, in case, for example, the orbiting scroll moves in an orbital manner at a high speed, excessive centrifugal force may apply to the auxiliary crank device, thereby possibly lowering durability of the auxiliary crank device.